#! /usr/bin/env python
#
def ch_to_rot13 ( ch ):

#*****************************************************************************80
#
## CH_TO_ROT13 converts a character to its ROT13 equivalent.
#
#  Discussion:
#
#    Two applications of CH_TO_ROT13 to a character will return the original.!
#
#    As a further scrambling, digits are similarly rotated using
#    a "ROT5" scheme.
#
#  Example:
#
#    Input:  Output:
#
#    a       n
#    C       P
#    J       W
#    1       6
#    5       0
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    30 January 2016
#
#  Author:
#
#    John Burkardt
#
#  Parameters:
#
#    Input, character CH, the character to be converted.
#
#    Output, character VALUE, the ROT13 equivalent of the character.
#
  i = ord ( ch )
#
#  [0:4] -> [5:9]
#
  if ( 48 <= i and i <= 52 ):
    value = i + 5
#
#  [5:9] -> [0:4]
#
  elif ( 53 <= i and i <= 57 ):
    value = i - 5
#
#  [A:M] -> [N:Z]
#
  elif ( 65 <= i and i <= 77 ):
    value = i + 13
#
#  [N:Z] -> [A:M]
#
  elif ( 78 <= i and i <= 90 ):
    value = i - 13
#
#  [a:m] -> [n:z]
#
  elif ( 97 <= i and i <= 109 ):
    value = i + 13
#
#  [n:z] -> [a:m]
#
  elif ( 110 <= i and i <= 122 ):
    value = i - 13
  else:
    value = i
 
  value = chr ( value )

  return value

def ch_to_rot13_test ( ):

#*****************************************************************************80
#
## CH_TO_ROT13_TEST tests CH_TO_ROT13.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    30 January 2016
#
#  Author:
#
#    John Burkardt
#
  import platform

  print ( '' )
  print ( 'CH_TO_ROT13_TEST' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  CH_TO_ROT13 "encodes" characters using ROT13' )
  print ( '  (and digits using ROT5).' )
  print ( '  A second application of the function returns the' )
  print ( '  original character.' )

  s1 = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
  s1_length = len ( s1 )
  s2 = ''
  s3 = ''

  for i in range ( 0, s1_length ):
    s2 = s2 + ch_to_rot13 ( s1[i] )
    s3 = s3 + ch_to_rot13 ( s2[i] )

  print ( '' )
  print ( '            CH  : %s' % ( s1 ) )
  print ( '      ROT13(CH) : %s' % ( s2 ) )
  print ( 'ROT13(ROT13(CH)): %s' % ( s3 ) )

  s1 = 'CH_TO_ROT13 "encodes" characters using ROT13'
  s1_length = len ( s1 )
  s2 = ''
  s3 = ''

  for i in range ( 0, s1_length ):
    s2 = s2 + ch_to_rot13 ( s1[i] )
    s3 = s3 + ch_to_rot13 ( s2[i] )

  print ( '' )
  print ( '            CH  : %s' % ( s1 ) )
  print ( '      ROT13(CH) : %s' % ( s2 ) )
  print ( 'ROT13(ROT13(CH)): %s' % ( s3 ) )
#
#  Terminate.
#
  print ( '' )
  print ( 'CH_TO_ROT13_TEST:' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  ch_to_rot13_test ( )
  timestamp ( )